Hydraulically controlled diaphragm pumps usually comprise a dosage head comprising a first part with a pumping chamber and a second part in which there is provided a hydraulic chamber which is filled with a hydraulic control fluid, and is separated from the pumping chamber by a diaphragm; as well as a dosage body comprising means for driving a piston of the pump in translation in the hydraulic chamber according to a given axis of translation.
It is common to equip the said pumps with a valve for regularization of pressure in the hydraulic chamber, in order in particular to avoid any damage to the diaphragm or blockage of the pump. The said valve is typically arranged in the vicinity of a highest point of the hydraulic chamber in the position of work of the pump, and comprises a hollow body which is in communication with the hydraulic chamber via a calibrated flap valve, the flap valve opening, when the pressure in the hydraulic chamber exceeds a threshold pressure, in order to discharge part of the fluid from the hydraulic chamber to the hollow body of the valve.
In addition, the valve can permit degassing of the air bubbles which are present in the hydraulic chamber.
However, the degassing is found to be limited because of the fact in particular of the reduced cross sections of the channels which connect the hydraulic chamber to the hollow body of the valve. In certain cases, bubbles can therefore remain wedged in the hydraulic chamber or in the channels which connect the said chamber to the hollow body of the valve. This is the case for example for pumps in which the dosage body is filled with air, thus giving rise to slight intake of air into the hydraulic chamber at each movement of translation of the piston, and thus to a relatively high concentration of bubbles in the hydraulic chamber.
However, the presence of air bubbles in the fluid in the hydraulic chamber and in the channels in connection with the hydraulic chamber tends to downgrade considerably the performance of the pumps, thus giving rise in particular to a substantial loss of their output. This disadvantage is increased further for pumps with small outputs.